An electronically scanned reflector (ESR) is an antenna that uses a phased array feed to illuminate a nearby reflector unit to generate one or more steerable antenna beams. Such antennas are being used increasingly in space-based applications such as, for example, satellite communications applications. As can be appreciated, antennas implemented in such remote, unmanned space applications can be difficult to calibrate. That is, should the antenna undergo mechanical distortions in space that negatively effect its ability to generate desired antenna beams, it is often difficult to compensate for these distortions after they have occurred because the antenna is so far away. In the past, calibration of space-based phased array antennas was generally performed during lengthy procedures involving a multitude of ground station measurements that were complicated by orbit velocities, signal to noise, and antenna location uncertainties. Such procedures are very complex and expensive to implement and the results are sometimes inaccurate.
Therefore, there is a need for a method and apparatus for calibrating an electronically scanned reflector antenna that can be used in space based antenna applications. The method and apparatus should be capable of compensating for mechanical distortions to a space based antenna to a relatively high degree of accuracy without requiring remote antenna pattern measurements. In addition, the method and apparatus should be relatively easy to implement and operate.